Question on how to determine rubber backing plate thickness

[Spoonful]

Hi All,

Simplified situation,

A piece of straight rubber block/strip, say 150mm (Lr) long by 30mm (Wr) wide. 30mm (Tr) thick, on top of it a steel plate os same size, 150mm (Ls) long, by 30mm (Ws)wide, its thickness (Ts) is to be determined.
Force f1 and f2, action on the edge of steel plate, downwards, so distance between f1 and f2 is 150mm. f1 and f2 is known, and f1=f2

Rubber hardness is known say 70 shore A
Steel design strength is know say 100 mpa.

question:
When f1 and f2 applied, rubber will tend to be compressed, because of the load is not exactly uniform, the plate will bend, say the allowable bending stress of the plate is 100mpa. what is the best way to model this situation to find out what thickness of the plate is required?

Thanks in advance

 

[desertfox]

Hi

If the rubber and steel are acting as one beam, you could convert the rubber section using the modulus of elasticity to obtain the equivalent thickness in steel and thereby do the beam calculation using one material, then subtract the converted thickness from the overall result and that will give you the steel section thickness you need.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[GregLocock]

I think the poorly quoted question from a textbook implies that there is a steel beam laying on a rubber layer laying on an infinitely stiff substrate. The answer, not surprisingly is in a textbook if you are too lazy to work it out. It is identically equal to a cantilever on an elastic foundation. I'd use Macaulay's method or whatever it is.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[3DDave]

I'd caution that rubber is not elastic in the sense that steel is. It is not compressible.

I've seen repeated examples where it is assumed that since rubber can deform, that trapping it will result in a flexible result. As an example, a blind hole with a rubber plug and steel piston is stiffer than if the rubber is replaced with steel.

You need to account for the amount of friction to determine what the actual load distribution will be. It runs a good chance of rupturing any bond between the rubber and the steel. In similar circumstances I've also seen tensile failure in the exposed edge of the rubber.

 

[desertfox]

Hi have a look at this link, this is what I thought your problem might be, scroll don till you find bending stresses

http://www.ecourses.ou.edu/cgi-bin/ebook.cgi?topic=me&chap_sec=06.1&page=theory

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein